Delay mounting sbin overlay

native/jni/core/bootstages.cpp

@@ -560,6 +560,9 @@ void post_fs_data(int client) {
 	write_int(client, 0);
 	close(client);
 
+	if (getenv("REMOUNT_ROOT"))
+		xmount(nullptr, "/", nullptr, MS_REMOUNT | MS_RDONLY, nullptr);
+
 	if (!check_data())
 		unblock_boot_process();
 

native/jni/init/early_mount.cpp

@@ -74,7 +74,7 @@ static void setup_block(const char *partname, char *block_dev) {
 	}
 }
 
-bool BaseInit::read_dt_fstab(const char *name, char *partname, char *fstype) {
+bool MagiskInit::read_dt_fstab(const char *name, char *partname, char *fstype) {
 	char path[128];
 	int fd;
 	sprintf(path, "%s/fstab/%s/dev", cmd->dt_dir, name);
@@ -152,10 +152,9 @@ void SARInit::early_mount() {
 if (mnt_##name) \
 	umount("/" #name);
 
-void BaseInit::cleanup() {
+void MagiskInit::cleanup() {
+	BaseInit::cleanup();
 	umount(SELINUX_MNT);
-	umount("/sys");
-	umount("/proc");
 	umount_root(system);
 	umount_root(vendor);
 	umount_root(product);

native/jni/init/init.cpp

@@ -26,13 +26,17 @@
 
 using namespace std;
 
+constexpr const char *init_applet[] =
+		{ "magiskpolicy", "supolicy", "magisk", nullptr };
+constexpr int (*init_applet_main[])(int, char *[]) =
+		{ magiskpolicy_main, magiskpolicy_main, magisk_proxy_main, nullptr };
+
 #ifdef MAGISK_DEBUG
 static FILE *kmsg;
 static int vprintk(const char *fmt, va_list ap) {
 	fprintf(kmsg, "magiskinit: ");
 	return vfprintf(kmsg, fmt, ap);
 }
-
 static void setup_klog() {
 	mknod("/kmsg", S_IFCHR | 0666, makedev(1, 11));
 	int fd = xopen("/kmsg", O_WRONLY | O_CLOEXEC);
@@ -46,11 +50,6 @@ static void setup_klog() {
 #define setup_klog(...)
 #endif
 
-constexpr const char *init_applet[] =
-		{ "magiskpolicy", "supolicy", nullptr };
-constexpr int (*init_applet_main[])(int, char *[]) =
-		{ magiskpolicy_main, magiskpolicy_main, nullptr };
-
 static bool unxz(int fd, const uint8_t *buf, size_t size) {
 	uint8_t out[8192];
 	xz_crc32_init();
@@ -113,6 +112,11 @@ static int dump_manager(const char *path, mode_t mode) {
 	return 0;
 }
 
+void BaseInit::cleanup() {
+	umount("/sys");
+	umount("/proc");
+}
+
 void BaseInit::re_exec_init() {
 	LOGD("Re-exec /init\n");
 	cleanup();
@@ -121,19 +125,22 @@ void BaseInit::re_exec_init() {
 }
 
 void LegacyInit::preset() {
+	full_read("/init", &self.buf, &self.sz);
+
 	LOGD("Reverting /init\n");
 	root = open("/", O_RDONLY | O_CLOEXEC);
 	rename("/.backup/init", "/init");
-	rm_rf("/.backup");
 }
 
 void SARInit::preset() {
+	full_read("/init", &self.buf, &self.sz);
+
 	LOGD("Cleaning rootfs\n");
 	root = open("/", O_RDONLY | O_CLOEXEC);
 	frm_rf(root, { "overlay", "proc", "sys" });
 }
 
-void BaseInit::start() {
+void MagiskInit::start() {
 	// Prevent file descriptor confusion
 	mknod("/null", S_IFCHR | 0666, makedev(1, 3));
 	int null = open("/null", O_RDWR | O_CLOEXEC);
@@ -144,9 +151,6 @@ void BaseInit::start() {
 	if (null > STDERR_FILENO)
 		close(null);
 
-	full_read("/init", &self.buf, &self.sz);
-	full_read("/.backup/.magisk", &config.buf, &config.sz);
-
 	preset();
 	early_mount();
 	setup_rootfs();

native/jni/init/init.h

@@ -14,9 +14,18 @@ struct raw_data {
 class BaseInit {
 protected:
 	cmdline *cmd;
-	raw_data self{};
-	raw_data config{};
 	char **argv;
+	void re_exec_init();
+	virtual void cleanup();
+public:
+	BaseInit(char *argv[], cmdline *cmd) : cmd(cmd), argv(argv) {}
+	virtual ~BaseInit() = default;
+	virtual void start() = 0;
+};
+
+class MagiskInit : public BaseInit {
+protected:
+	raw_data self{};
 	int root = -1;
 	bool load_sepol = false;
 	bool mnt_system = false;
@@ -24,34 +33,31 @@ protected:
 	bool mnt_product = false;
 	bool mnt_odm = false;
 
-	virtual void preset() {};
-	virtual void early_mount() {}
+	virtual void preset() = 0;
+	virtual void early_mount() = 0;
 	void setup_rootfs();
 	bool read_dt_fstab(const char *name, char *partname, char *fstype);
 	bool patch_sepolicy();
-	void cleanup();
-	void re_exec_init();
-
+	void cleanup() override;
 public:
-	BaseInit(char *argv[], cmdline *cmd) : cmd(cmd), argv(argv) {}
-	virtual ~BaseInit() = default;
-	virtual void start();
+	MagiskInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {};
+	void start() override;
 };
 
-class LegacyInit : public BaseInit {
+class LegacyInit : public MagiskInit {
 protected:
 	void preset() override;
 	void early_mount() override;
 public:
-	LegacyInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {};
+	LegacyInit(char *argv[], cmdline *cmd) : MagiskInit(argv, cmd) {};
 };
 
-class SARInit : public BaseInit {
+class SARInit : public MagiskInit {
 protected:
 	void preset() override;
 	void early_mount() override;
 public:
-	SARInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {};
+	SARInit(char *argv[], cmdline *cmd) : MagiskInit(argv, cmd) {};
 };
 
 static inline bool is_lnk(const char *name) {
@@ -63,3 +69,4 @@ static inline bool is_lnk(const char *name) {
 
 void load_kernel_info(cmdline *cmd);
 int dump_magisk(const char *path, mode_t mode);
+int magisk_proxy_main(int argc, char *argv[]);

native/jni/init/rootfs.cpp

@@ -1,11 +1,13 @@
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/mount.h>
 #include <fcntl.h>
 
 #include <magisk.h>
 #include <utils.h>
 
 #include "init.h"
+#include "flags.h"
 #include "magiskrc.h"
 
 #ifdef USE_64BIT
@@ -37,7 +39,7 @@ constexpr const char wrapper[] =
 "exec /sbin/magisk.bin \"$0\" \"$@\"\n"
 ;
 
-void BaseInit::setup_rootfs() {
+void MagiskInit::setup_rootfs() {
 	bool patch_init = patch_sepolicy();
 
 	if (cmd->system_as_root) {
@@ -125,55 +127,13 @@ void BaseInit::setup_rootfs() {
 	link_dir(sbin, rootdir);
 	close(sbin);
 
-	LOGD("Mount /sbin tmpfs overlay\n");
-	xmount("tmpfs", "/sbin", "tmpfs", 0, "mode=755");
-	sbin = xopen("/sbin", O_RDONLY | O_CLOEXEC);
-
-	char path[64];
-
-	// Create symlinks pointing back to /root
-	DIR *dir = xfdopendir(rootdir);
-	struct dirent *entry;
-	while((entry = xreaddir(dir))) {
-		if (entry->d_name == "."sv || entry->d_name == ".."sv)
-			continue;
-		sprintf(path, "/root/%s", entry->d_name);
-		xsymlinkat(path, sbin, entry->d_name);
-	}
-
-	// Dump binaries
-	mkdir(MAGISKTMP, 0755);
-	fd = xopen(MAGISKTMP "/config", O_WRONLY | O_CREAT, 0000);
-	write(fd, config.buf, config.sz);
-	close(fd);
-	fd = xopen("/sbin/magiskinit", O_WRONLY | O_CREAT, 0755);
+	// Dump magiskinit as magisk
+	fd = xopen("/sbin/magisk", O_WRONLY | O_CREAT, 0755);
 	write(fd, self.buf, self.sz);
 	close(fd);
-	if (access("/system/apex", F_OK) == 0) {
-		LOGD("APEX detected, use wrapper\n");
-		dump_magisk("/sbin/magisk.bin", 0755);
-		patch_socket_name("/sbin/magisk.bin");
-		fd = xopen("/sbin/magisk", O_WRONLY | O_CREAT, 0755);
-		write(fd, wrapper, sizeof(wrapper) - 1);
-		close(fd);
-	} else {
-		dump_magisk("/sbin/magisk", 0755);
-		patch_socket_name("/sbin/magisk");
-	}
-
-	// Create applet symlinks
-	for (int i = 0; applet_names[i]; ++i) {
-		sprintf(path, "/sbin/%s", applet_names[i]);
-		xsymlink("/sbin/magisk", path);
-	}
-	xsymlink("/sbin/magiskinit", "/sbin/magiskpolicy");
-	xsymlink("/sbin/magiskinit", "/sbin/supolicy");
-
-	close(rootdir);
-	close(sbin);
 }
 
-bool BaseInit::patch_sepolicy() {
+bool MagiskInit::patch_sepolicy() {
 	bool patch_init = false;
 
 	if (access(SPLIT_PLAT_CIL, R_OK) == 0) {
@@ -214,3 +174,86 @@ bool BaseInit::patch_sepolicy() {
 
 	return patch_init;
 }
+
+#ifdef MAGISK_DEBUG
+static FILE *kmsg;
+static int vprintk(const char *fmt, va_list ap) {
+	fprintf(kmsg, "magiskinit: ");
+	return vfprintf(kmsg, fmt, ap);
+}
+static void setup_klog() {
+	int fd = xopen("/proc/kmsg", O_WRONLY | O_CLOEXEC);
+	kmsg = fdopen(fd, "w");
+	setbuf(kmsg, nullptr);
+	log_cb.d = log_cb.i = log_cb.w = log_cb.e = vprintk;
+	log_cb.ex = nop_ex;
+}
+#else
+#define setup_klog(...)
+#endif
+
+int magisk_proxy_main(int argc, char *argv[]) {
+	setup_klog();
+
+	raw_data config;
+	raw_data self;
+
+	full_read("/sbin/magisk", &self.buf, &self.sz);
+	full_read("/.backup/.magisk", &config.buf, &config.sz);
+
+	xmount(nullptr, "/", nullptr, MS_REMOUNT, nullptr);
+
+	unlink("/sbin/magisk");
+	rm_rf("/.backup");
+
+	LOGD("Mount /sbin tmpfs overlay\n");
+	xmount("tmpfs", "/sbin", "tmpfs", 0, "mode=755");
+	int sbin = xopen("/sbin", O_RDONLY | O_CLOEXEC);
+
+	char path[64];
+
+	// Create symlinks pointing back to /root
+	{
+		unique_ptr<DIR, decltype(&closedir)> dir(xopendir("/root"), &closedir);
+		struct dirent *entry;
+		while((entry = xreaddir(dir.get()))) {
+			if (entry->d_name == "."sv || entry->d_name == ".."sv)
+				continue;
+			sprintf(path, "/root/%s", entry->d_name);
+			xsymlinkat(path, sbin, entry->d_name);
+		}
+	}
+
+	// Dump binaries
+	mkdir(MAGISKTMP, 0755);
+	int fd = xopen(MAGISKTMP "/config", O_WRONLY | O_CREAT, 0000);
+	write(fd, config.buf, config.sz);
+	close(fd);
+	fd = xopen("/sbin/magiskinit", O_WRONLY | O_CREAT, 0755);
+	write(fd, self.buf, self.sz);
+	close(fd);
+	if (access("/system/apex", F_OK) == 0) {
+		LOGD("APEX detected, use wrapper\n");
+		dump_magisk("/sbin/magisk.bin", 0755);
+		patch_socket_name("/sbin/magisk.bin");
+		fd = xopen("/sbin/magisk", O_WRONLY | O_CREAT, 0755);
+		write(fd, wrapper, sizeof(wrapper) - 1);
+		close(fd);
+	} else {
+		dump_magisk("/sbin/magisk", 0755);
+		patch_socket_name("/sbin/magisk");
+	}
+
+	// Create applet symlinks
+	for (int i = 0; applet_names[i]; ++i) {
+		sprintf(path, "/sbin/%s", applet_names[i]);
+		xsymlink("/sbin/magisk", path);
+	}
+	xsymlink("/sbin/magiskinit", "/sbin/magiskpolicy");
+	xsymlink("/sbin/magiskinit", "/sbin/supolicy");
+
+	setenv("REMOUNT_ROOT", "1", 1);
+	execv("/sbin/magisk", argv);
+
+	return 1;
+}